Writer: Natisha Hales
Each year thousands of New Mexicans travel to Elephant Butte Reservoir for fishing, water skiing and other water sports. But it's not just a recreational area; Elephant Butte is the main water supply to the Mesilla Valley.
st visitors don't realize is that a large portion of Elephant Butte's average inflow is lost due to evaporation.
In the interest of water conservation, three engineering students at New Mexico State University have conducted research aimed at more accurate measurement of evaporative loss from Elephant Butte. A more accurate knowledge of evaporation would lead to better predictions for determining water allotments and allocation.
Alex Herting, Tim Farmer and Jordan Evans took the first step toward more reliable mapping of the evaporative loss at Elephant Butte by combining what is known as the bulk-aerodynamic method with remote sensing and Geographical Information Systems (GIS) technology.
"The existing method for estimating evaporation is pretty crude," explained civil engineering professor Phillip King. King was the students' adviser during the research project.
The bulk-aerodynamic method may provide a more accurate estimate and uses a variety of factors such as the temperature of water, relative humidity, wind speed and air temperature to estimate evaporation.
With the use of remote sensing, satellite images that contain large amounts of data may be used to estimate evaporation more accurately. GIS technology will use satellite images and other data to determine the area of the lake. When all of this data is combined, evaporative loss can be analyzed.
A method known as pan evaporation is currently used at Elephant Butte. With this method, a pan is placed near the reservoir and readings are taken from the pan as the water level goes down and the pan heats up. The measurement is multiplied by a pan coefficient to estimate the depth of lake evaporation.
However, there is an assumption that evaporation is the same over the entire surface area of the lake and that the relationship between pan and lake evaporation remains the same throughout the year. In addition, extra heat through the walls of the pan during certain times of the year yields unreliable, inaccurate results.
Although the students concluded that pan evaporation is not the most accurate method, they also concluded that further research is needed on using the bulk-aerodynamic method.
King said follow-up research is in progress, conducted by Max Bleiweiss, an atmospheric scientist at White Sands Missile Range. "He is a local expert and put the most work into this study and helping the students," he said. "We are very grateful for his input."
Supplements to this research include ground-based measurements and the use of spectral bands to map evaporative loss.
The students' project was partly funded by the New Mexico Water Resources Research Institute at NMSU.
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